1. Field of the Invention
The present invention relates to a method for production of thin films and, more particularly, a method for producing thin films of strontium titanate on desired substrates without use of complex procedures.
2. Description of the Prior Art
In general, strontium titanate, SrTiO.sub.3, has been utilized as a dielectric material for various electronic devices such as, for example, capacitors because of its superior properties. For such applications, strontium titanate is preferably used in the form of thin films to make the best use of its properties.
As a method for formation of thin films of strontium titanate on substrates, there have been so far known various methods such as, for example, a sputtering process (Nikkei microdevices, 1991, June, pp. 78-86), a plasma deposition process (JP-A-1-175714), and a hydrothermal, electrochemical method (JAPANESE JOURNAL OF APPLIED PHYSICS, Vol. 30, No. 1B (1990), pp. L123).
However, the processes of the above prior art for formation of thin films of strontium titanate have various problems awaiting a solution. For example, the first two, i.e., the sputtering process and plasma deposition process, have the following problems: (a) They requires use of expensive complex equipment, resulting in considerable increase of plant investment; (b) it is difficult with such a process to deposit thin films on substrates with a complex configuration other than a plate form; and (c) the material for substrates is limited only to those which can stand high temperatures as the substrate is subjected to high temperatures. The last one, i.e., hydrothermal electrochemical method, includes such problems that it is required to use a substrate made of metallic titanium or coated with metallic titanium, that it requires complex steps, and that the substrate is considerably limited in material as the formation of thin films is carried out under conditions of high temperature and pressure.
Recently, an interesting work related to production of a dielectric ceramic material has been reported in "Journal of Materials Science" 25 (1990), 1169-1183. This report teaches that barium titanate can be produced in the form of powder hydrolyzing titanium alkoxide in a solution containing barium ions at low temperatures. However, it suggests nothing about possibility of production of thin films of dielectric materials.